Ultrasonic data-processing systems

ABSTRACT

The present invention relates to data-processing systems based upon the diffraction properties of a coherent radiation near a focus. The data-processing system in accordance with the invention comprises at least one ultrasonic tank containing a fluid wherein coherent ultrasonic radiation propagates; this tank contains a modulating object on which there are transcribed the data being processed; ultrasonic focussing means provides by means of a Fourier transform the spatial frequency spectrum of said object.

United States Patent 11 1 [111 3,795,801

Broussaud Mar. 5, 1974 [54] ULTRASONIC DATA-PROCESSING 3,699,805 10/1972Bayre 73/676 SYSTEMS OTHER PUBLICATIONS [751 Gwrges Bmussaud Pans FranceKnollman et al.: Variable Focus Liquid Filled l-lydroa- [73] Assignee:Thomson-C811, P i France coustic Lens. Journal of the Acoustic Ser. ofAm. pp.

253-261, Vol. 49, No. 1, 1971. [22] Filed: June 8, 1972 [21] Appl. No.:261,104 Primary ExaminerFelix D. Gruber v Attorney, Agent, orFirm--Cushman, Darby & [30] Foreign Application Priority Data CushmanJune 15,1971 France 71.21602 [57] ABSTRACT 1 Cl 131/05 2 The presentinvention relates to data-processing sys 324/77 340/5 H terns based uponthe diffraction properties of a coher- [51] ll!- Ci G06g 7/19, B0612)3/04 a t radiation near a focus, [58] held of "g The data-processingsystem in accordance with the invention comprises at least oneultrasonic tank containing a fluid wherein coherent ultrasonic [56]References cued radiation propagates; this tank contains a modulatingUNITED STATES PATENTS object on which there are transcribed the databeing 3,431,462 4/1969 Muenow et al. 340/5 H processed; ultrasonicfocussing means provides by 2,803,128 8/1957 Peterman 73/67.6 an of aFourier transform the spatial frequency Trommler..... H pectrum of saidobject 3,168,659 2/1965 Bayre et al.... 340/8 L 3,295,629 1/1967Papadakis 340/8 L 24 Claims, 9 Drawing Figures mum/110R GENERATORPATENTED 51974 3,795,801

mm 2 I}? 5 GENERATOR PATENTED 51974 3,795,801

SHEET 3 [IF 5 PATENIEBHAR 51974 SHEET 5 [IF 5 SEEM. E03

ULTRASONIC DATA-PROCESSING SYSTEMS The present invention relates todata-processing systems whose operation is based upon the diffractionproperties of coherent radiation. Systems of this kind are used in theoptical field in order to carry out operations such as spectral analysisand spatial filtering in this case, the data take the form of opticallymodulating objects which are associated with one or more diffractingcells. In traversing these objects and cells, the complex amplitudes ofan optical radiation experience physical transformations which are veryclosely related with the Fourier transform. As far as data transcriptionin concerned, the starting point can take the form of modulating objectswhich carry an arbitrary graphic pattern or the mark left on a surfaceby an impression, but it frequently happens that the data areconstituted by electrical signals. The exploitation of the properties ofoptical diffraction in a data-processing system gives rise to problemsbecause the manufacturing and assembly tolerances must be in the sameorder of magnitude as the wavelength of the radiation used. In addition,at the point in the system where data transcription takes place, thedetails of the modulating object must be sufficiently fine and close inorder to observe an effective spread-out of the diffraction pattern.These difficulties mean that the construction of the modulating objectsis a more delicate operation than the ensuing processing it results thatthe data transcription time, too, is the longest part of the process.Another difficulty inherent in optical processing systems is that theaccuracy of the results depends very much upon what measures are takento eliminate parasitic phase-modulation effects. This leads to the useof perfectly flat and isotropic data-carriers as well as to lenses ofhigh optical quality a precaution which often has to be taken is toimmerse the data-carrier in a fluid which has substantially therefraction index of the data-carrier, so that no phase errors areintroduced.

The foregoing observations show that optical dataprocessing systems aredelicate and expensive instruments which do not generally enablereal-time processing of data.

In order to overcome these drawbacks, the invention provides for thesubstitution of the electromagnetic waves occurring in the opticalsystems, by ultrasonic waves propagating through a fluid. The wavelengthof the ultrasonic waves is chosen in order to establish a compromisebetween the complexity of the data transcription devices and theprocessing capacity of the other component parts of the system.

According to the present invention there is provided an ultrasonic dataprocessing system comprising at least one ultrasonic tank containing afluid, a source of ultrasonic radiation positioned for emitting throughsaid fluid a beam of ultrasonic energy, at least one diffraction cellpositioned for receiving said beam, and ultrasonic detection meanspositioned for collecting the ultrasonic energy emerging from saiddiffraction cell said diffraction cell comprising stigmatic ultrasonicmeans positioned for focussing said beam onto a spectral planepertaining to said cell and ultrasonic modulating object meanspositioned on the path of said beam for modulating said ultrasonicenergy in accordance with data supplied to said processing system saidultrasonic energy being constituted by ultrasonic longitudinal wavestravelling through said fluid said ultrasonic longitudinal waves being,upon irradiation of said ultrasonic modulating object means, reradiatedfor projec tion onto said spectral plane. I

For a better understanding of the invention and to show how the same maybe carried into effect reference will be made to the ensuing descriptionand the attached figures in which FIG. 1 illustrates a first example ofa data-processing system in accordance with the invention.

FIG. 2 illustrates a second example of a dataprocessing system inaccordance with the invention.

FIG. 3 illustrates an isometric view of a spectrumgenerating ultrasonictank in accordance with the invention, equipped with multichannel datatranscription means.

FIG. 4 illustrates a variant embodiment of the datatranscription meansshown in FIG. 3.

FIG. 5 is an isometric view of a spectrum-generating ultrasonic tankdesigned to receive data for processing, in the form of a reliefimpression applied to a supporting surface of the tank.

FIG. 6 is a variant embodiment of the device shown in FIG. 5.

FIG. 7 illustrates a phase-contrast arrangement in accordance with theinvention.

FIG. 8 illustrates a device for constructing a filter in accordance withthe invention.

FIG. 9 illustrates a real-time data-processing system for producing theauto-correlation function of .a signal or the cross-correlation functionof two signals.

Analog data-processing systems are generally based upon the diffractionphenomena near a focus.

In coherent optical systems, when light radiation is focussed forforming a spherical wave whose wavefronts are centred on a point, thereis a fundamental relationship between the complex amplitudes of theillumination received in the focal plane, and the complex amplitudes ofthe luminance function along any one of these wavefronts. If x and y arethe coordinates of a point upon a selected wavefront and S (x, y) thecomplex amplitude of the vibration carried by the radiation at thispoint, then it can be shown that the complex amplitude E (u, v) of thevibration received at a point having the coordinates u and v in thefocal plane, is given This integral is the expression for atwo-dimensional Fourier transform which also has a reciprocal propertyin this formula, R represents the radius of curvature of the wavefrontand A the wavelength of the radiation.

Optical data-processing systems of course perform operations of thiskind by means of coherent light vibrations, but it is equally possible,as we shall see hereinafter, to carry out the same operations just asnaturally by making use, and this indeed more simply, of mechanicalvibrations carried in the form of longitudinal ultrasonic waves in acompressible fluid.

The basic cell of an ultrasonic data-processing system in accordancewith the invention is thus essentially con stituted by an ultrasonictank containing a compressible fluid and a coherent ultrasonic radiationsource producing radiation of wavelength M. In the tank, a device isimmersed for focussing the ultrasonic radiation on a spectral plane, andin the neighbourhood of this device there is introduced a modulatingobject upon which there have previously been transcribed the data forprocessing. This kind of cell, followed by an appropriate radiationdetector, constitutes an ultrasonic spectrum analyser which can processsignals represented by a one or two dimensional function. However,without departing from the scope of the invention, it is equallypossible to add to the first processing cell another cell in order toeffect two successive Fourier transforms in this case, thedata-processing system be comes a double-diffraction system which canfilter spatial frequencies of one set of data as a function of otherdata introduced between the cells in the form ofa filter.

A first embodiment ofa data-processing system in accordance with theinvention has been schematically illustrated in FIG. 1. In its mostcomprehensive form it comprises a double-diffraction ultrasonic system.It incorporates an ultrasonic tank 1 containing a compressible fluid 2wherein longitudinal ultrasonic waves are propagated without dispersionand excessive attenuation. An electromechanical transducer 3 connectedto an electrical generator 4, radiates a parallel ultrasonic beam ofwavelength A which propagates through the fluid 2 from right to left inFIG. 1. An afocal device imthe left hand of filter 12 and comprises aconvergent ultrasonic lens 13 with a focal lengthf A plane 14perpendicular to the plane of the figure is disposed in relation to theobject 7 and the lenses l3 and 8 in such a 5 manner as to pick up, aftera double diffraction, the ulbution of vibrational amplitude as thatemerging from the object 7. However, if we take into account the actionof the filter 12 and bear in mind, too, the properties of the Fouriertransform, the ultrasonic image received in the plane 141 will present adistribution of I complex vibrational amplitudes which is expressed bymersed in the fluid 2 enlarges the transverse section of the beamradiated by the transducer 3 this device is made up of a pair ofconvergent ultrasonic lenses 5-6. These lenses can be constituted by acavity with convex faces enclosing a fluid which is capable oftransmitting the ultrasonic waves at a propagation velocity lower thanthat of the fluid 2. By way of a non-limitative example, the fluid 2 canbe constituted by water whilst the fluid filling the lenticular cavities5-6 is methylene iodide. The ultrasonic radiation emerging from the lens6 illuminates an ultrasonic modulating means constituted by an object 7which transmits the incident radiation with complex vibrationalamplitudes representing the data being processed. The radiation modulatdby the ultrasonic modulating object 7 passes through a convergentultrasonic lens 8 arranged so that its two foci are located respectivelyin the plane of the object 7 and in a spectral plane 9 perpendicular tothe plane of FIG. 1 the focal length of the lens 8 is equal to f,, and,as FIG. 1 shows, this lens focusses the parallel beam coming from thelens 6 in a geometric way in the plane 9.

In fact, if we take into account the presence of the ultrasonicmodulating object 7 and the effects of the diffraction, then it will berealised that the distribution of the complex vibration amplitudesreceived by the plane 9 represents the spectrum of the spatialfrequencies of the distribution of the complex vibrational amplitudesemerging from the object 7. Consequently, lens 8 is a stigmaticultrasonic means building up with the plane of the object 7, and thespectral plane 9, a first diffraction cell having the property ofdisplaying within plane 9 the Fourier transform of the distributionemerging from the object 7, the latter being representative of the databeing processed.

If an ultrasonic detector 10 is immersed in the fluid 2 and connected toan indicating instrument 11 in order to scan the spectral plane 9, theelements located to the right of the plane 9 form a spectral analyser.

On the other hand, as FIG. 1 shows, more efficient data-processing canbe effected by means of a second diffraction cell made up of theelements represented at the left of the spectral plane 9. This secondcell lies on the convolution integral. More precisely, if thecoordinates of the object plane are (x,,, y,,), if those of the spectralplane 9 are (u, v) and if (x y,) are the coordinates of the image plane141, then we can write where g (x,-, y,) is the distribution of complexamplitudes in the image plane f(x y is the distribution of complexamplitudes of the object h (x,, y,) is the distribution of complexamplitudes in the image plane in relation to the response of thediffractive system to the Dirac delta function.

The foregoing integral can be written in condensed form as follows Inaddition, if the Fourier transforms of the functions g, fand h arerespectively G (u, v), F (u, v) and H (u, v), then from the theorem ofthe Fourier transform we know that we can write the foregoingexpressions as G (u, v) F (u, v) H (u, v).

This simple expression shows us in a simple manner how the spectrum ofthe spatial frequencies G (u, v) transmitted by a filter 12 results fromthe multiplication of the spectrum of the spatial frequences F (u, v)feeding the filter 12 by its own transfer function H (u, v).Consequently, if we arrange a radiation detector 15 and a display device16 at the end of the doublediffraction system shown in FIG. 1, then anapparatus is created which will make it possible to arbitrarily filterthe spatial frequencies and in particular to establish a correlationbetween data suitably transcribed at ultrasonic modulating object means7 and at a filter 12 performing a similar function.

The special feature of the double-diffraction ultrasonic system shown inFIG. 1 is that it utilises stigmatic ultrasonic means such as lenses 8and 13 in order to make parallel beams converge in planes 9 and 14. InFIG. 2, another version of the double-diffraction system in accordancewith the invention can be seen.

In this simplified version, the elements have been given referencescorresponding to those of the similar elements in FIG. 1. The system ofFIG. 2 differs from that of FIG. 1 by its use of solid ultrasonic lenses5, 8 and 13 which, whilst being convergent lenses, have a concaveprofile. By way of non-limitative example, if the fluid 2 is water, thelenses 5, 8 and 13 are made of polystyrene, which material propagatescompressive ultrasonic waves with a velocity 1.8 times higher than thevelocity of these same waves in water. Since the lenses are made of asolid material, it must be ensured that this material has the leastpossible degree of transmission for transverse waves because theselatter constitute a parasitic vibratory mode this condition is amplysatisfied if polystyrene or paraffin is used.

As far as the arrangement of the lenses 5, 8 and 13 is concerned, itwill be seen from a consideration of FIG. 2 that the lens 5 focuses theultrasonic radiation at the focus P the lens 8 of the first diffractioncell forms at P, the image of P and the lens 13, of the seconddiffraction cell, forms the image of the object 7 in the image plane 14;the focal length of the lens 13 isf The double-diffraction system ofFIG. 2 operates on the same principle as that of FIG. 1 but using lenseswhich are simpler to manufacture and are not required in such largenumbers. The systems of FIGS. 1 and 2 can employ stigmatic ultrasonicmeans made of spherical or cylindrical lenses, depending upon whether ornot the Fourier transforms carried out are twodimensional, or singledimensional ones. Furthermore, as concerns the stigmatic ultrasonicmeans building up the diffraction cells the invention is not limited tothe use of ultrasonic lenses because, as we shall see at a later pointin the description, they can equally well be replaced by mirror systems.The projection of longitudinal ultrasonic waves into an ultrasonic tankcan give rise to parasitic reflections these can be eliminated by liningthe walls of the tank with materials which absorb ultrasound FIG. 2illustrates the application of this kind of lining 17, to the verticalwall of the tank 1.

Hitherto, we have left aside the business of the transcription of theultrasonic modulating data, that is to say the creation of the objectmeans 7 and the filter 12. In FIG. 3, an example of aspectrum-generating ultrasonic tank capable of the real-time processingby single-variable Fourier transform, ofa set of separate electricalsignals S,,;S and S constituting the data, can be seen. The signals S5,; and S are, for example, physiological signals utilised for theplotting of an electrocardiogram or an electro-encephalogram they mayequally well be geophysical signals supplied from a seismograph.

The ultrasonic processing system of FIG. 3 comprises an ultrasonic tank1 containing a fluid 2 whose surface 9 is parallel to the referencetrihedron OXYZ. A set of transducers 3 immersed in the fluid 2 radiatesultrasonic energy travelling parallel to OZ this energy is contained indirectional ultrasonic beams these are received by the paraboliccylindrical face of a first reflector 5. A pair of reflectors 8 havingreflective faces in the form of elliptical cylinders, respectively focusthe ultrasonic beams along focal lines aligned end to end in the surface9 in order to illustrate the trajectory of the ultrasonic energy, raysindicated in broken line and converging at the point P have been shown.Between the surface 9, which is a spectral plane, and reflectors 5 and8, a modulating object 7 is arranged which can move in the direction ofthe arrow between two carrier rollers 18. This object is produced by themechanical engraving of a band of thermoplastic material passing betweena cylinder 19 and a set of engraving cutters 21 these latter areoperated by electromechanical transducers which receive the electricalinformation for processing. The viscosity-temperature characteristic ofthermoplastic materials, exhibits a discontinuity at a giventemperature. This property can be exploited in order to deform athermoplastic substrate raised to said temperature, through the actionof extremely small forces; if the thermoplastic substrate is cooledimmediately after having undergone this deformation, it retains a printwhich does not change afterwards.

Having chosen a thermoplastic material in which ultrasonic waves aretransmitted at a velocity differing from the velocity of propagationcharacterizing the environment, it is possible, thanks to the printingaction of cutters 21 and under the control of the signals 8,, S and S tolinearly modulate the thickness of the band along a generatrix of thecylinder 19 the cylinder 19, by its rotation, transports the band pastthe engraving tools 20, 21, giving rise to the engraved tracks 22. Thedeformation of the band is more readily brought about by raising it tothe temperature referred to hereinbefore to this end, heating means,which have not been shown, are associated with the cylinder 19 or thecutters 21. After engraving, the printed tracks 22 enter the fluid 2 andact, between the rollers 18, as phase objects 7. The ultrasonicradiation whose phase is modulated by these variable-thickness tracks,is projected into the surface plane 9 in the form of spectral patterns23 of rectangular shape which can be detected by means of a hydrophonescanning the surface 9. It goes without saying that the spectral planecan likewise be located below the surface 9 of the fluid 2 and that anydetector arrangement other than a hydrophone, could be used to pick upthe spatial frequencies of the signals S S and S The fineness of prints22 as well as the positional tolerances governing the elementconstituting the data-processing ultrasonic tank shown in FIG. 3, haveto be in the same order of magnitude as the wavelength of the ultrasonicradiation in the fluid 2.

This condition makes the best ultrasonic frequency range for working,that between 30 and 300 MC/s, and in the case of water this correspondsto a wavelength A ranging between and 5 microns. The utilisation ofsubstantially higher ultrasonic frequencies, would give rise to themultiple drawbacks encountered in optical processing systems, whilst theutilisation of substantially lower ultrasonic frequencies would mean areduction in the quantity of data which could be processed.

The electromechanical data transcription system by the ultrasonicmodulating object means shown in FIG. 3, produces a modulating object 7whose engraved print is a function of only one variable, in the case ofeach of the three tracks provided.

FIG. 4, shows a system wherein ultrasonic modulating object meansprovide a data transcription which is based upon the utilisation ofelectrostatic forces, in order to deform the thermoplastic substrate 7.The system comprises a comb whose conductive teeth 122, insulated byspacers, receive voltages from an electrical generator 24, which areapplied between a set of electrodes 124 belonging to the comb and aheated metal cylinder 19. The input 25 of the generator is supplied withthe data for transcription and successively supplies potentialdistributions along the comb, which deform the substrate 7 in accordancewith a succession of parallel lines stepped in the direction of verticaldisplacement. These ultrasonic modulating object means enable animpression to be formed upon the substrate 7, which is a function of twovariables. If the device shown in FIG. 4- is employed in the processingsystem of FIG. 3, in order to produce a two-dimensional Fouriertransform, only one transducer 3 need be used, which is centred inrelation to the reflectors 5 and 8 and has a verti cal axis ofrevolution.

The data transcription devices illustrated in FIGS. 3 and 4 are designedfor data supplied in the form of electrical signals.

In FIG. 5, a spectrum-generating ultrasonic tank can be seen which isdesigned to receive data for processing, in the form on an existingimpression the relief pattern of which has only two significant levels.This kind of network of striata is encountered in particular whenprocessing digital impressions or again when the data for processing areconstituted by a text or block in the form of a relief.

The system shown in FIG. 5 comprises an ultrasonic tank 1 containing afluid 2 in a lateral wall of the tank and below the level of the fluid,are assembled ultrasonic modulating object means comprising animpression receiver device embodying one or more layers 27 and 28 ofelastic materials. The layers 27 and 28 are used to match the impedanceof the fluid 2 to that of the material of which the substrate 29carrying the impression is made, which substrate is applied against theexternal face 26 for insuring data transfer.

At the point of intimate contact between the projecting parts of theimpression and the face 26, the ultra sonic energy is transmittedwithout reflection but at the intertices, where there is no contact, theultrasonic energy experiences major reflection. This process ofultrasonic modulation by reflection requires that a uniform ultrasonicbeam be directed from the interior of the fluid 2 onto the face 26. Tothis end, an ultrasonic transducer 3 immersed in the fluid 2 emitsultrasonic radiation propagating in the direction 30 the radiationselectively reflected at the face 26 is propagated in the reversedirection and subsequently passes up towards the surface of the fluid 2along the trajectory 32. A semi-reflective plate 31 is immersed in thefluid 2 in order to direct the modulated ultrasonic energy towards thetop of the tank the ultrasonic energy coming from the transducer 3 forthe most part passes through the plate 31 whilst the non-transmittedenergy fraction is absorbed by an appropriate coating 33 located at thebottom of the tank. Between the surface of the fluid 3 and the plate 31,the modulated ultrasonic radiation encounters a convergent ultrasoniclens 34 which projects to the surface of the fluid 2 the spectrum of thespatial frequencies 35 of the impression applied against the receiverface 26. Plate 31 may be made of any layer having an acousticalimpedance differing from that of the surrounding medium.

In FIG. 6, a spectrum-generating system can be seen whose constituentparts are practically identical with those of the system shown in FIG. 5to simplify matters, the same references have been used in both figures.The element 36 is an ultrasonic generator not shown in FIG. 5.

From the foregoing, we have seen that the impression-receivers of FIGS.5 and 6 constitute ultrasonic modulating object means operating byreflection, whilst those of FIGS. 1 to 3 operate by transmission. In thecase of modulation by reflection, it is the modulus of the complexvibrational amplitude in the right section of the beam, whichexperiences the modulation, the argument remaining substantiallyconstant. In the case of modulation by transmission, the reversesituation applies the ultrasonic modulating object is then a phaseobject which is substantially transparent to ultrasonic waves.

Although the use of a phase object in no Way impedes the formation of aneasily perceptible spectrum of spatial frequencies, in adouble-diffraction ultrasonic system it may be desirable for the objectto be an amplitude-modulating object.

In FIG. 7, a phase-contrast ultrasonic arrangement can be seenassociated with the phase object 37 which, in an exit plane OXY, canproduce a non-uniform distribution of ultrasonic vibrational amplitudes.This ar' rangement, which is normally immersed in a fluid, essentiallyhas the same structure as the doublediffraction ultrasonic system ofFIG. 2. It comprises an ultrasonic source 38 illuminating the phaseobject 37 across a convergent ultrasonic lens 39. A filter is arrangedperpendicularly to the axis OZ at the location where the lens 39 in thegeometric sense forms the point image of the source 38; anotherconvergent ultrasonic lens 41 arranged behind the filter 30, forms theultrasonic image of the object 37 in the plane XOY.

The filter 40 is a phase plate divided into four quadrants the thicknessof the plate changes abruptly in passing from one quadrant to the next,in order to introduce a phase difference of half a wavelength in therespective ultrasonic vibrations passing through these quadrants. Theresult is that the spectrum of spatial frequencies projected onto thefilter 40 by the combination of the elements 38, 39 and 37 is multipliedby a filter function of constant modulus and whose argument changes by1r in passing from one quadrant to the next.

At the output of the filter 40, the filtered spectrum passes through thelens 41 which projects the image of the object 37 this image correspondsto a distribution of complex vibrational amplitudes whose modulus variesin the x and y senses in correspondence with the phase variations whichcharacterize the distribution of the complex vibrational amplitudesemerging from the object 37. Bearing in mind the law governing thefiltering function of the filter 40, it can be shown that the processingwhich the phase object 37 experiences is a two-variable Hilberttransform.

The arrangement shown in FIG. 7, provides an example of data-processingby filtering of the spatial fre quencies, in which the filter design isparticularly simple. In the more general case where the aim is to effecta convolution between two sets of data or where it is desired todetermine by correlation the positions occupied in a text by a givencharacter, the problem arises of engraving the filter so that its filterfunction is the Fourier transform of a predetermined function or thecomplex conjugate of this transform.

In FIG. 8, an apparatus can be seen which is intended for theconstruction of a filter suitable for the case of either convolution orcorrelation.

In order to construct a filter of this kind, there are available, apriori, data representing the Dirac delta response h (x,-, y,) and thetechnique is to engrave a substrate capable of imposing upon ultrasonicradiation passing through it, a phase-modulation which represents eitherthe Fourier transform function H (u, v) or h (x y or the conjugatefunction H (u, v) ofI-I (u, v). To this end, an engraving table 42 canbe employed to the top of which a blank substrate d3 has been attached.A slide 45 on the table 42 guides a carriage 46 carrying a sliding bar47 the bar 47 can be displaced perpendicularly and parallel to the slide45 in order that its ends can synchronously scan identical fields one ofwhich is aligned above the substrate 43 and the other above anultrasonic tank 51 carried by the table 42. An engraving head 48,controlled electrically, is assembled at one of the ends of the bar 4'7and a hydrophone 49 with an ultrasonic detector probe 50, at the other.The electrical signals produced by the hydrophone 49 are received by ananalyser circuit 52 which controls the engraving head 48 as a functionof their amplitude or phase in relation to the ultrasonic fieldgenerated in the tank 51. The tank 51 is similar to the ones shown inFIGS. 3 and 5. At the surface of the fluid which it contains, itproduces a distribution H (u, v) of complex vibrational amplitudes,which represents the Fourier transform of the data (x y,) supplied tothe transcription device. This distribution is analysed by the detector50 whose free end is flush with the surface of the fluid the engravinghead 48 imprints in the substrate 43 an impression corresponding to theanalysis effected by the detector 50 and, because these two elementsdisplace in synchronism with one another, it can readily be arrangedthat the impression engraved in the substrate represents in full thefunction H (u, 1/). It should be pointed out that the engraving head 48can be equipped with an engraving tool displacing perpendicularly to thesubstrate but it is also possible to use an optical engraving methodfollowed by chemical processing in order to produce at the surface of aphotographic substrate a relief corresponding to the desiredphasemodulation. If the data-processing system is used as a correlator,the filter can be constituted by a Fourier hologram. In this case whichprovides an impression corresponding to the conjugate of the functionl-I(u,v), the tank must contain a further ultrasonic source whichsuperimposes upon the spectrum I-I(u,v) of spatial frequencies of themodulating object, a reference ultrasonic wave. The device shown in FIG.8 offers the possibility of producing a filter by engraving itsimpression in the form of successive lines. The time taken to engrave afilter means that it is not possible to obtain the processed results atthe same instant at which the data are supplied to the processingsystem.

In FIG. 9, a correlator system can be seen which comprises twoultrasonic tanks, 57 and 69, optically coupled to one another, and anoptical device for producing the correlation function of data whosespectral analysis is effected by the ultrasonic tanks. The data forprocessing are applied in the form of electrical signals F and H totranscription devices 62 and 66 which are capable of recording onthermoplastic substrates 60 and 68, impressions which act as ultrasonicmodulating object means. The driving and heating of the substrates 60and 68 are effected by cylinders 61 and 67 they are carried beneath thelevel of the fluid filling the vessels 57 and 69, by means of guiderollers 63 and 72. Each tank contains an ultrasonic radiation source 64or 73 located at one of the foci of an elliptical-section reflector 65or 74. An electrical generator 85 supplies the sources 64 and 73. Thanksto the reflectors 65 and 74 which act as ultrasonic stigmatic means, theultrasonic radiation components are made to converge at the other focuslocated in the neighbourhood of the surface of the fluid contained ineach of the tanks 57 and 69 the horizontal portions of the ultrasonicmodulating objects 60 and 68 being located close to the exit pupils ofthe reflectors 65 and 74, there are picked up at the surfaces of thetanks 57 and 69 distributions of complex ultrasonic amplitudes whichcorrespond to the spatial frequency spectra of the signals F and H. Inorder to pick up and transmit these distributions, a coherent lightsource 53, through the medium of the mirror 55 associated with an afocaldevice 54, vertically illuminates the top region of the tank 57 wherethe ultrasonic spectrum of the signal F is projected. This region isoccupied by a cell 59 which comprises a thin film of oil separated fromthe fluid of the tank 57 by an extremely thin impermeable membrane.Under the action of the radiation pressure of the ultrasonic vibrations,the top face of the oil film deforms and reflects the incident lightwith a phase-modulation which corresponds to the distribution ofultrasonic energy as picked up by the cell 59. The tank 69 is likewiseequipped with a cell 71 similar to that 59. To this end, an opticalcoupling device links the top faces of the two cells. This couplingdevice comprises two semi-reflecting plates 56 and 75 between whichthere have been arranged two lenses 78 and 79 to form an afocal opticalsystem a diaphragm 77, at the focus of the lenses 78 and 79, selects thezero order light radiation diffracted by the cell 59, the higher orders,represented in dotted fashion, being blocked by the diaphragm 77. Thelight incident upon the top face of the cell 71 has already experienceda first phase modulation under the action of the cell 59 the light whichemerges from the cell 71 thus contains two superimposedphase-modulations. The two modulations produced successively by thepassage of the light through the ultrasonic tanks 57 and 69 correspondrespectively to the spatial frequency spectra of the signals F and H sothat the resultant modulation of the light emerging from the cell 71corresponds to the product of the spectra projected by the tanks 57 and69. This observation shows that the set of elements of FIG. 9, justdescribed, is equivalent to the first part of a double-diffractioncorrelator including the associated filter. In other words, theultrasonic tank 57 can be considered as containing the object and thefirst diffraction system cell, whilst the ultrasonic tank 69 is a filtergenerator. In order to obtain the desired correlation function, all thatremains to be done is to carry out a second Fourier transform and thisis what is done by the optical system which picks up the light reflectedby the cell 71 after its transition through the semireflective plate 75.This optical system which builds up a second diffraction cell comprisesa mirror 76 and a convergent lens 80 in the focal plane of which aselecting diaphragm 81 is mounted. The energy passing the diaphragm 81is picked up by a lens 82 and supplied to a plane 83 where thecorrelation function is displayed.

Where it is a correlation function which is to be produced, thoseskilled in the art will appreciate that the filter action mustconstitute the conjugate of the function representing the spectrum ofthe signal associated with the filter. This condition can readily besatisfied by using a Fourier hologram to produce the filter. To thisend, in the ultrasonic tank 69 there is immersed a point ultrasonicenergy source 84 which obliquely illuminates the bottom face of the cell71 this source 84 is excited in the same way as the source 73 by thegenerator 83. Because of the action of the source 84, the reflection ofthe light by the cell 71 takes place in accordance with the laws ofhologram reconstruction, giving rise to diffracted waves or orders 0,+1, and l. The l order gives rise in the focal plane of the lens 80 to areal image which is transmitted by the diaphragm 81 the and +1diffracted orders follow the dotted trajectories and are blocked by thediaphragm 81.

The correlation function appearing in the exit plane 83 is across-correlation function between the signals F and H. It is alsopossible to obtain the autocorrelation function of one of these signals.F for example, by transferring the substrate 611 from tank 57 to tank 69in this case, the transcription device 66, 67 and the substrate 68 aresuperfluous. In closing, it is worth while mentioning that it isadvantageous to pulseoperate the ultrasonic tanks. In this case, it isuseful to arrange for the light source to operate synchronously with theinput of ultrasonic energy to the cells 59 and 71 this synchronisationcan be achieved by triggering the operation of the ultrasonic generator85 with a pulse 86 furnished by the source 53.

What I claim is:

1. An ultrasonic data processing system comprising at least oneultrasonic tank containing a fluid, at least one source of ultrasonicradiation (3,5) positioned for emitting through said fluid a beam ofultrasonic energy, at least one diffraction cell (6,9) positioned forreceiving said beam, and ultrasonic detection means positioned forcollecting the ultrasonic energy emerging from said diffraction cellsaid diffraction cell comprising stigmatic ultrasonic means (8)positioned for focussing said beam onto a spectral plane (9) pertainingto said cell and ultrasonic modulating object means (7) embodying saiddata positioned on the path of said beam for modulating said ultrasonicenergy; said ultrasonic energy being constituted by ultrasoniclongitudinal waves travelling through said fluid said ultrasoniclongitudinal waves being upon irradiation of said ultrasonic modulatingobject means, re-radiated for projection onto said spectral plane.

2. A system as claimed in claim 1, wherein said ultrasonic detectionmeans comprise a supplementary diffraction cell (13, 14) and ultrasonicfilter means (12) said ultrasonic filter means being arranged betweenthe spectral plane (9) of said one diffraction cell and saidsupplementary diffraction cell.

3. A system as claimed in claim 1, wherein said source comprises atleast one electromechanical transducer immersed in said fluid, andultrasonic generator means for exciting said transducer.

4. A system as claimed in claim 1, wherein said ultrasonic detectionmeans comprise at least one electromechanical transducer connected toindicator means for displaying the intensity of the ultrasonic radiationpicked up by said transducer.

5. A system as claim 1, wherein the internals walls, of said tank areexposed to said ultrasonic radiation being lined with a layer ofmaterial absorbing the incident ultrasonic energy.

6. A system as claimed in claim 1, wherein said stigmatic ultrasonicmeans are constituted by convergent ultrasonic lenses.

7. A system as claimed in claim 6, wherein each of said lenses comprisesa lenticular cavity filled with a fluid said ultrasonic longitudinalwaves propagating through the fluid filling said lenses at a velocitydiffering from that which they have in the fluid filling said ultrasonictank.

8. A system as claimed in claim 6, wherein said lenses are cut from asolid material selectively transmitting longitudinal ultrasonicvibrations the profile of said lenses having a minimum thickness at thecentre said solid material transmitting said ultrasonic longitudinalwaves at a velocity higher than that which they have in the fluidfilling said ultrasonic tank.

9. A system as claimed in claim 1, wherein said ultrasonic modulatingobject means comprise a phase object cut from a solid materialtransmitting said ultrasonic longitudinal waves at a velocity differingfrom that which they have in said fluid.

10. A system as claimed in claim 9, wherein said ultrasonic modulatingobject means further comprise a phase-contrast ultrasonic arrangement(39, 40, 41) associated with said phase object (37).

11. A system as claimed in claim 10, wherein said phase-contrastarrangement is a double-diffraction system comprising two furtherdiffraction cells in succes' sion and a phase-contrast filter (40)arranged between said two further diffraction cells.

12. A system as claimed in claim 1, wherein said stigmatic ultrasonicmeans are constituted by at least one ultrasonic curved mirror.

13. A system as claimed in claim 12, wherein said curved mirror is acylindrical mirror.

14. A system as claimed in claim 12, wherein said curved mirror has anelliptical profile.

15. A system as claimed in claim 14, wherein said stigmatic ultrasonicmeans further comprise another curved mirror having a parabolic profile,and associated homofocal with said curved mirror.

16. A system as claimed in claim 1, wherein said ultrasonic modulatingobject means (26, 27, 28) is an ultrasonic reflective modulatorcomprising a stack of plates with parallel faces, one of said facesbeing in contact with said fluid and a further one of said facesprojecting outside the ultrasonic tank containing said fluid said databeing constituted by a relief impression applied against said furtherface ;said system further comprising a semitransparent plate (31)immersed in said fluid between said stack and said source saidsemi-reflecting plate transmitting the ultrasonic radiation emitted bysaid source toward said stack and also transmitting back toward saidstigmatic ultrasonic means the ultrasonic radiation reflected from saidstack in relation with the hollow parts of said relief impression.

17. An ultrasonic data processing system comprising at least oneultrasonic tank containing a fluid, at least one source of ultrasonicradiation positioned for emitting through said fluid a beam ofultrasonic energy, at least one diffraction cell positioned forreceiving said beam, ultrasonic detection means (10, 13, 14, 1S)positioned for collecting the ultrasonic energy emerging from saiddifiraction cell, and transcription means (19, 20, 21) for transcribingsaid data; said diffractional cell including stigmatic ultrasonic means(8) positioned for focussing said beam onto a spectral plane pertainingto said cell, and ultrasonic modulating object means (7) embodying saiddata positioned on the path of said beam for modulating said ultrasonicenergy said transcription means comprising means (20,21) forelectromechanically engraving a thermoplastic substrate constitutingsaid ultrasonic modulating object means and means (19) for displacingsaid substrate in relation to said engraving means said engraving meanscomprising at least one engraving cutter integral with an electromechanical transducer receiving an electrical signal representativeof said data, said ultrasonic energy being constituted by longitudinalwaves travelling through said fluid said ultrasonic longitudinal wavesbeing upon irradiation of said ultrasonic modulating object means,re-radiated for projection onto said spectral plane.

18. An ultrasonic data processing system comprising at least oneultrasonic tank containing a fluid, at least one source of ultrasonicradiation positioned for emitting through said fluid a beam ofultrasonic energy, at least one diffraction cell positioned forreceiving said beam, ultrasonic detection means (10, 13, 14, 15)positioned for collecting the ultrasonic energy emerging from saiddiffraction cell, and transcription means (19, 122, 123) fortranscribing said data; said diffraction cell including stigmaticultrasonic means (8) positioned for focusing said beam onto a spectralplane pertaining to said cell, and ultrasonic modulating object means(7) embodying said data positioned on the path of said beam formodulating said ultrasonic energy said transcription means comprising aplurality of electrodes (122) aligned with one another and flush withthe surface of a thermoplastic substrate, and a mating electrode (19)constituted by a cylinder transporting said substrate said transcriptionmeans further comprising electrical means (24) controlled by said data,for applying between said cylinder and said electrodes electricalvoltages said electrical voltages deforming said substrate under theaction of electrostatic forces said cylinder being equipped with heatingmeans for raising said substrate to a temperature at which the viscosityof the thermoplastic substrate is substantially reduced; said ultrasonicenergy being constituted by longitudinal waves travelling through saidfluid said ultrasonic longitudinal waves being upon irradiation of saidultrasonic modulating object means, re-radiated for projection onto saidspectral plane.

19. An ultrasonic data processing system comprising a first and a secondultrasonic diffraction cell each of said diffraction cells being locatedin an ultrasonic tank containing a fluid, at least one ultrasonic sourceimmersed in said fluid, stigmatic ultrasonic means (64, 65, 73, 74) forfocussing the ultrasonic energy emitted by said source, onto a spectralplane close to the surface of said fluid, a modulating object immersedin said fluid between said stigmatic ultrasonic means and said spectralplane, and an optical reflector element deformable under the action ofthe ultrasonic energy received by said spectral plane said processingsystem further comprising a coherent optical radiation sourceilluminating the reflector element of said first diffraction cell, anoptical coupling device (56, 78, 77, 79, linking the reflecting faces ofsaid optical reflector elements, and an optical diffraction cell (80,81) picking up the optical radiation emerging from the optical reflectorelement of said second diffraction cell.

20. A system as claimed in claim 19, wherein said optical couplingdevice comprises an afocal optical system having a common focal planeand a diaphragm arranged in said focal plane said diaphragm selectivelytransmitting that portion of the optical radiation emerging from thereflector element of said first diffraction cell, corresponding to thezero diffraction order.

21. A system as claimed in claim 19, wherein said optical diffractioncell comprises optical focussing means for focussing the radiationemerging from the optical reflector element of said second diffractioncell, onto a spectral plane, and a diaphragm located in the said lastmentioned spectral plane said diaphragm selectively transmitting thatportion of the optical radiation emerging from the optical reflectorelement of said second diffraction cell corresponding to one of thediffraction orders other than the zero order.

22. A system as claimed in claim 19, wherein data transcription means(61, 62, 66, 67) are associated with said first and second ultrasonicdiffraction cells.

23. A system as claimed in claim 19, wherein data transcription means(61, 62) are associated with one of said first and second ultrasonicdiffraction cells the modulating objects of said first andvsecondultrasonic diffraction cells being constituted by separate portions ofthe thermoplastic substrate engraved by said transcription means.

24. A system as claimed in claim 19, wherein the optical reflectorelement of said second ultrasonic diffraction cell receives anultrasonic reference beam emitted by a supplementary ultrasonic sourceimmersed in said fluid.

1. An ultrasonic data processing system comprising : at least oneultrasonic tank containing a fluid, at least one source of ultrasonicradiation (3,5) positioned for emitting through said fluid a beam ofultrasonic energy, at least one diffraction cell (8,9) positioned forreceiving said beam, and ultrasonic detection means positioned forcollecting the ultrasonic energy emerging from said diffraction cell ;said diffraction cell comprising : stigmatic ultrasonic means (8)positioned for focussing said beam onto a spectral plane (9) pertainingto said cell and ultrasonic modulating object means (7) embodying saiddata positioned on the path of said beam for modulating said ultrasonicenergy; said ultrasonic energy being constituted by ultrasoniclongitudinal waves travelling through said fluid ; said ultrasoniclongitudinal waves being upon irradiation of said ultrasonic modulatingobject means, re-radiated for projection onto said spectral plane.
 2. Asystem as claimed in claim 1, wherein said ultrasonic detection meanscomprise a supplementary diffraction cell (13, 14) and ultrasonic filtermeans (12) ; said ultrasonic filter means being arranged between thespectral plane (9) of said one diffraction cell and said supplementarydiffraction cell.
 3. A system as claimed in claim 1, wherein said sourcecomprises at least one electromechanical transducer immersed in saidfluid, and ultrasonic generator means for exciting said transducer.
 4. Asystem as claimed in claim 1, wherein said ultrasonic detection meanscomprise at least one electromechanical transducer connected toindicator means for displaying the intensity of the ultrasonic radiationpicked up by said transducer.
 5. A system as claim 1, wherein theinternals walls, of said tank are exposed to said ultrasonic radiationbeing lined with a layer of material absorbing the incident ultrasonicenergy.
 6. A system as claimed in claim 1, wherein said stigmaticultrasonic means are constituted by convergent ultrasonic lenses.
 7. Asystem as claimed in claim 6, wherEin each of said lenses comprises alenticular cavity filled with a fluid ; said ultrasonic longitudinalwaves propagating through the fluid filling said lenses at a velocitydiffering from that which they have in the fluid filling said ultrasonictank.
 8. A system as claimed in claim 6, wherein said lenses are cutfrom a solid material selectively transmitting longitudinal ultrasonicvibrations ; the profile of said lenses having a minimum thickness atthe centre ; said solid material transmitting said ultrasoniclongitudinal waves at a velocity higher than that which they have in thefluid filling said ultrasonic tank.
 9. A system as claimed in claim 1,wherein said ultrasonic modulating object means comprise : a phaseobject cut from a solid material transmitting said ultrasoniclongitudinal waves at a velocity differing from that which they have insaid fluid.
 10. A system as claimed in claim 9, wherein said ultrasonicmodulating object means further comprise a phase-contrast ultrasonicarrangement (39, 40, 41) associated with said phase object (37).
 11. Asystem as claimed in claim 10, wherein said phase-contrast arrangementis a double-diffraction system comprising two further diffraction cellsin succession and a phase-contrast filter (40) arranged between said twofurther diffraction cells.
 12. A system as claimed in claim 1, whereinsaid stigmatic ultrasonic means are constituted by at least oneultrasonic curved mirror.
 13. A system as claimed in claim 12, whereinsaid curved mirror is a cylindrical mirror.
 14. A system as claimed inclaim 12, wherein said curved mirror has an elliptical profile.
 15. Asystem as claimed in claim 14, wherein said stigmatic ultrasonic meansfurther comprise another curved mirror having a parabolic profile, andassociated homofocal with said curved mirror.
 16. A system as claimed inclaim 1, wherein said ultrasonic modulating object means (26, 27, 28) isan ultrasonic reflective modulator comprising a stack of plates withparallel faces, one of said faces being in contact with said fluid and afurther one of said faces projecting outside the ultrasonic tankcontaining said fluid ; said data being constituted by a reliefimpression applied against said further face ;said system furthercomprising a semitransparent plate (31) immersed in said fluid betweensaid stack and said source ; said semi-reflecting plate transmitting theultrasonic radiation emitted by said source toward said stack and alsotransmitting back toward said stigmatic ultrasonic means the ultrasonicradiation reflected from said stack in relation with the hollow parts ofsaid relief impression.
 17. An ultrasonic data processing systemcomprising : at least one ultrasonic tank containing a fluid, at leastone source of ultrasonic radiation positioned for emitting through saidfluid a beam of ultrasonic energy, at least one diffraction cellpositioned for receiving said beam, ultrasonic detection means (10, 13,14, 15) positioned for collecting the ultrasonic energy emerging fromsaid diffraction cell, and transcription means (19, 20, 21) fortranscribing said data; said diffractional cell including : stigmaticultrasonic means (8) positioned for focussing said beam onto a spectralplane pertaining to said cell, and ultrasonic modulating object means(7) embodying said data positioned on the path of said beam formodulating said ultrasonic energy ; said transcription means comprisingmeans (20,21) for electromechanically engraving a thermoplasticsubstrate constituting said ultrasonic modulating object means and means(19) for displacing said substrate in relation to said engraving means ;said engraving means comprising at least one engraving cutter integralwith an electromechanical transducer receiving an electrical signalrepresentative of said data, said ultrasonic energy being constituted bylongitudinal waves travelling through said fluid ; said ultrasoniclongitudinal waves being upon irradiation of said ultrasonic modulatingobject means, re-radiated for projection onto said spectral plane. 18.An ultrasonic data processing system comprising : at least oneultrasonic tank containing a fluid, at least one source of ultrasonicradiation positioned for emitting through said fluid a beam ofultrasonic energy, at least one diffraction cell positioned forreceiving said beam, ultrasonic detection means (10, 13, 14, 15)positioned for collecting the ultrasonic energy emerging from saiddiffraction cell, and transcription means (19, 122, 123) fortranscribing said data; said diffraction cell including : stigmaticultrasonic means (8) positioned for focusing said beam onto a spectralplane pertaining to said cell, and ultrasonic modulating object means(7) embodying said data positioned on the path of said beam formodulating said ultrasonic energy ; said transcription means comprisinga plurality of electrodes (122) aligned with one another and flush withthe surface of a thermoplastic substrate, and a mating electrode (19)constituted by a cylinder transporting said substrate : saidtranscription means further comprising electrical means (24) controlledby said data, for applying between said cylinder and said electrodeselectrical voltages ; said electrical voltages deforming said substrateunder the action of electrostatic forces ; said cylinder being equippedwith heating means for raising said substrate to a temperature at whichthe viscosity of the thermoplastic substrate is substantially reduced;said ultrasonic energy being constituted by longitudinal wavestravelling through said fluid ; said ultrasonic longitudinal waves beingupon irradiation of said ultrasonic modulating object means, re-radiatedfor projection onto said spectral plane.
 19. An ultrasonic dataprocessing system comprising : a first and a second ultrasonicdiffraction cell ; each of said diffraction cells being located in anultrasonic tank containing a fluid, at least one ultrasonic sourceimmersed in said fluid, stigmatic ultrasonic means (64, 65, 73, 74) forfocussing the ultrasonic energy emitted by said source, onto a spectralplane close to the surface of said fluid, a modulating object immersedin said fluid between said stigmatic ultrasonic means and said spectralplane, and an optical reflector element deformable under the action ofthe ultrasonic energy received by said spectral plane ; said processingsystem further comprising a coherent optical radiation sourceilluminating the reflector element of said first diffraction cell, anoptical coupling device (56, 78, 77, 79, 75) linking the reflectingfaces of said optical reflector elements, and an optical diffractioncell (80, 81) picking up the optical radiation emerging from the opticalreflector element of said second diffraction cell.
 20. A system asclaimed in claim 19, wherein said optical coupling device comprises anafocal optical system having a common focal plane and a diaphragmarranged in said focal plane ; said diaphragm selectively transmittingthat portion of the optical radiation emerging from the reflectorelement of said first diffraction cell, corresponding to the zerodiffraction order.
 21. A system as claimed in claim 19, wherein saidoptical diffraction cell comprises optical focussing means for focussingthe radiation emerging from the optical reflector element of said seconddiffraction cell, onto a spectral plane, and a diaphragm located in thesaid last mentioned spectral plane ; said diaphragm selectivelytransmitting that portion of the optical radiation emerging from theoptical reflector element of said second diffraction cell correspondingto one of the diffraction orders other than the zero order.
 22. A systemas claimed in claim 19, wherein data transcription means (61, 62, 66,67) are associated with said first and second ultrasonic diffractioncells.
 23. A system as claimed in claim 19, wherein data transcriptionmeans (61, 62) are associated with one of said first and secondultrasonic diffraction cells ; the modulating Objects of said first andsecond ultrasonic diffraction cells being constituted by separateportions of the thermoplastic substrate engraved by said transcriptionmeans.
 24. A system as claimed in claim 19, wherein the opticalreflector element of said second ultrasonic diffraction cell receives anultrasonic reference beam emitted by a supplementary ultrasonic sourceimmersed in said fluid.